Method for Operating a Magnetic-Inductive Flowmeter and Corresponding Magnetic-Inductive Flowmeter

Abstract

A magnetic-inductive flowmeter and a method for operating the flowmeter are disclosed. The flowmeter includes: a measuring tube for guiding an electrically conductive medium; magnetic field devices which can be energized separately with excitation currents for generating at least one magnetic field passing through the measuring tube; measuring electrodes for capturing a measuring voltages induced in the medium; and a control and evaluation unit for generating the magnetic field by energizing at least one of the magnetic field devices and for calculating the volume flow of the medium through the measuring tube. The method includes: applying excitation currents to the magnetic field devices; capturing measurement voltages; and determining flow-dependent transfer factors from the excitation currents and the measurement voltages caused by the excitation currents; and calculating the volume flow of the medium from the transfer factors.

1 . A method for operating a magnetic-inductive flowmeter, having a measuring tube for guiding an electrically conductive medium, having a plurality of magnetic field devices, which can be energized separately with excitation currents, for generating at least one magnetic field passing through the measuring tube at least partially perpendicular to the direction of flow of the medium, with a plurality of measuring electrodes for capturing a plurality of measuring voltages induced in the medium, and with a control and evaluation unit for generating the magnetic field by energizing at least one of the magnetic field devices and for calculating the volume flow of the medium through the measuring tube, the method comprising:
 applying a plurality of excitation currents to the plurality of the magnetic field devices;   capturing a plurality of measurement voltages is captured;   determining a plurality of flow-dependent transfer factors from the excitation currents and the measurement voltages caused by the excitation currents, wherein a each of the transfer factors is a ratio of a proportion of a measurement voltage caused by an excitation current to a magnitude of this the excitation current; and   calculating the volume flow of the medium from the transfer factors.   
     
     
         2 . The method according to  claim 1 , wherein several of the plurality of magnetic field devices are simultaneously subjected to the plurality of excitation currents. 
     
     
         3 . The method according to  claim 1 , wherein the volume flow of the medium is calculated from a linear combination of the transfer factors; and
 wherein the transfer factors are weighted by weighting factors.   
     
     
         4 . The method according to  claim 1 , wherein the volume flow of the medium is calculated using a first non-linear function in the transfer factors; and
 wherein the transfer factors in the non-linear function are weighted by weighting factors.   
     
     
         5 . The method according to  claim 4 , wherein normalized transfer factors are calculated using a known or measured kinematic viscosity of the medium;
 wherein the normalized transfer factors are mapped non-linearly with the aid of a second non-linear function to an estimated value for a total Reynolds number; and   wherein the volume flow is then calculated using the function, taking into account the kinematic viscosity of the flowing medium.   
     
     
         6 . The method according to  claim 4 , wherein the first non-linear function and the second non-linear function are formed by an artificial neural network including:
 an input layer with at least a number of input neurons corresponding to a number of the transfer factors used as input variables;   an output layer with at least one output neuron for outputting at least the volume flow of the medium as output variable; and   at least one intermediate layer with at least two neurons; and wherein the artificial neural network is trained with calibration data.   
     
     
         7 . The method according to  claim 1 , wherein only a determined number or a determined percentage of the transfer factors which are of a highest order is used to determine the volume flow, or that only transfer factors which are above a determined percentage value of the value range of all transfer factors are used to determine the volume flow. 
     
     
         8 . The method according to  claim 1 , wherein n magnetic field devices are energized to determine the volume flow and m measurement voltages are captured and m*n transfer factors are determined. 
     
     
         9 . The method according to  claim 8 , wherein in n measurement cycles carried out in succession with n linearly independent excitation current vectors, each with the excitation currents are applied to the magnetic field devices; and
 wherein the magnetic field devices which have a non-zero excitation current are applied simultaneously in a measurement cycle.   
     
     
         10 . The method according to  claim 9 , wherein in one measurement cycle exactly one excitation current is different from zero, so that m transfer factors can be determined immediately in one measurement cycle. 
     
     
         11 . The method according to  claim 9 , wherein the excitation currents in the excitation current vectors are selected in such a way that one of the excitation current vectors as row vectors or column vectors is orthogonal; and
 wherein the measurement voltages captured in the measurement cycles are cross-correlated with the excitation currents in order to implement an optimal filtering.   
     
     
         12 . The method according to  claim 9 , wherein the excitation currents in the excitation current vectors are selected such that an excitation current matrix formed from the excitation current vectors as row vectors or column vectors is orthogonal;
 wherein the excitation current matrix is obtained by a Householder transformation of a freely selected excitation current vector; and   wherein preference is given to those excitation current matrices which have a low variance in the values of the matrix elements.   
     
     
         13 . The method according to  claim 9 , wherein the non-zero excitation currents in the excitation current vectors have the same amplitude, in particular and have the maximum amplitudes provided for in the operation of the magnetic-inductive flowmeter. 
     
     
         14 . The method according to  claim 1 , wherein the electrochemical voltage components at the measurement voltages are determined and adjusted measurement voltages are calculated by subtracting the electrochemical voltage components from the measured voltages; and
 wherein the method is performed with the adjusted measured voltages.   
     
     
         15 . A magnetic-inductive flowmeter, comprising:
 a measuring tube for guiding an electrically conductive medium;   a plurality of magnetic field devices which can be energized separately with excitation currents for generating at least one magnetic field passing through the measuring tube at least partially perpendicular to the direction of flow of the medium;   a plurality of measuring electrodes for capturing a plurality of measuring voltages induced in the medium; and   a control and evaluation unit for generating the magnetic field by energizing at least one of the magnetic field devices and for calculating the volume flow of the medium through the measuring tube;   that wherein the control and evaluation unit is designed such that the magnetic-inductive flowmeter performs a method during operation, the method including the following steps:
 applying a plurality of excitation currents to the plurality of the magnetic field devices; 
 capturing a plurality of measurement voltages; 
 determining a plurality of flow-dependent transfer factors from the excitation currents and the measurement voltages caused by the excitation currents, wherein each of the transfer factors is a ratio of a proportion of a measurement voltage caused by an excitation current to a magnitude of the excitation current; and 
 calculating the volume flow of the medium from the transfer factors. 
   
     
     
         16 . The magnetic-inductive flowmeter according to  claim 15 , wherein at least as many excitation current sources are present as different excitation currents are required to act on the magnetic field devices, so that the magnetic field devices can be acted on simultaneously with an excitation current. 
     
     
         17 . The magnetic-inductive flowmeter according to  claim 15 , wherein fewer excitation current sources are present than different excitation currents are required to act on the magnetic field devices; and
 wherein the excitation current sources are sequentially connected to the magnetic field devices by means of a demultiplexer arrangement, so that the magnetic field devices can be subjected to an excitation current in succession in time or partly simultaneously and partly in succession in time.   
     
     
         18 . The magnetic-inductive flowmeter according to  claim 15 , wherein at least as many voltage measuring devices are present as there are different measuring voltages to be captured, so that the measuring voltages can be captured simultaneously. 
     
     
         19 . The magnetic-inductive flowmeter according to  claim 15 , wherein fewer voltage measuring devices are present than different measuring voltages are present; and
 wherein the voltage measuring devices are switched sequentially to the measuring electrodes by means of a multiplexer arrangement, so that the measuring voltages can be detected in succession in time or partly simultaneously and partly in succession in time.